Labat’s classic
al technique
Labat's classical approach was the most popular technique before the development of new approaches more easily to perform and less uncomfortable to patients. Originally described as a paresthesia method, the advent of nerve stimulation has increased the effectiveness, patient discomfort and reduced complications and number of needle insertions. The procedure sequence consists of five phases, depicted in Figure 8. Nerve stimulation is began using a current of 2-3 mA (2 Hz, 0.1-0.3 msec), and reduced to 0.3-0.5 mA before injection of local anesthetic. The patient lays supine, with the limb to be blocked at 30º abduction. The pubic tubercle is identified by palpation and a 1.5 cm long line is drawn laterally and caudally (the point of injection being at the end of the later). The classical approach consists of carrying out three consecutive movements of the needle until the tip of the needle is placed over the top of the obturator foramen, where the nerve runs before splitting into its two terminal branches. Using a 22G 8 cm long needle, the skin is penetrated perpendicularly and the needle is advanced until it makes contact with the inferior border of the superior pubic branch at a depth of 2-4 cm. During the second phase, the needle is slightly withdrawn and then slipped along the anterior pubic wall (another 2-4 cm); following this it is redirected anterior/posterior. Finally, the needle is withdrawn again and slightly redirected (cephalically and laterally) at an angle of 45º for another 2-3 cm until contractions of the thigh adductor muscles are observed.
This technique can be simplified by eliminating the second movement of the needle. Hence, after making contact with the pubic branch, the needle can be redirected 45º laterally to the obturator foramen (Figure 9).
Paravascular selective inguinal block
This technique consists of selective block of the two branches of the obturator nerve (anterior and posterior), performed at the inguinal level and slightly more caudad than the previously described techniques.[61] The femoral artery and the tendon of the long adductor muscle at the pubic tubercle are identified. For tendon identification, extreme leg abduction is required, Figure 10. A line is drawn over the inguinal fold from the pulse of the femoral artery to the tendon of the long adductor muscle. The needle is inserted at the mid-point of this line at an angle of 30º anterior/posterior and cephalically,Figure 11. By following the needle a few centimeters in depth, via the long adductor muscle, twitching responses from the long adductor and gracilis muscles are easily detectable on the posterior and medial aspect of the thigh. Subsequently, the needle is inserted deeper (0.5-1.5 cm) and slightly laterally over the short adductor muscle until a response from the major adductor muscle is obtained and can be visualized on the posterior-medial aspect of the thigh. Following needle insertion, infiltration of 5-7 ml local anesthetic is recommended. Occasionally, a more caudal division of the obturator nerve is found; hence, the two branches are located within the same location at the inguinal fold and two different motor responses may be observed with a single stimulation (injection).